The invention relates to a method in connection with a secondary coating line, in which method a fibre, fibres or fibre bundles are unwound from payoff reels and guided to a press by which a secondary sheath is formed around the fibre(s) or the fibre bundles and grease is fed into the secondary sheath, and in which method the assembly formed by the secondary sheath and the fibre(s) or the fibre bundles is pulled at a constant rate and low tension to a winding device through cooling means. The invention further relates to an arrangement in connection with a secondary coating line.
At present, the methods and arrangements described above are well known in the cable industry. Examples of known solutions include the solutions disclosed in U.S. Pat. No. 4,893,998, DE patents 27 57 786, 32 39 024 and 34 25 649, DE published application 38 22 566 and Fl patent 94989.
One of the most important characteristics of a secondary coating line is to be able to control the difference in length between a fibre and a secondary sheath and to achieve a stable secondary coating after the process. Particularly the extent of after-contraction taking place after cooling of a coating of an S-Z stranded and straightened construction affects the quality of the final product, in other words the optic cable. In principle, the previously known solutions are satisfactory in the above respect, but progress in technology has led to increasingly higher rates, which, in turn, has resulted in dramatically greater line lengths. The great line lengths take up much space, which makes installation more difficult when a line is being renovated, for example, and thus increases the costs.
An object of the invention is to achieve good control and adjustment of the difference in length at rates higher than the current ones and small after-contraction of secondary coating without substantially increasing the line length. This is achieved by the method and arrangement of the invention. The method of the invention is characterized in that the difference in length between the fibre(s) or the fibre bundles and the secondary sheath is adjusted by adjusting fibre tension by moving the fixing point between the fibre(s) or the fibre bundles and-the-secondary sheath along a straight part formed in the relaxation part. The arrangement of the invention, in turn, is characterized in that the difference in length between the fibre(s) or the fibre bundles and the secondary sheath is arranged to be adjusted by adjusting fibre tension by moving the fixing point between the fibre(s) or the fibre bundles and the secondary sheath along a straight part formed in the relaxation part by using wheel structures (8, 10).
An advantage of the invention is that the process can be controlled in an extremely inexpensive way at line rates higher than the current ones and the line length can be maintained at the current level. Another advantage of the invention is that the control of the difference in length enables the current adjustment based on tension adjustment to operate properly. Another advantage of the invention is its simplicity; the invention is inexpensive to implement and use.